The goal of this fellowship proposal is to characterize the olfactory particulate guanylyl cyclase (pGC) using rat chemosensory cilia isolated by calcium shock as a model. The cGMP signaling pathway is less understood than the cAMP pathway. However, its critical role in most cell types, especially neuronal cells, has been highlighted since it is the target of the diffusible messenger molecules nitric oxide (NO) and carbon monoxide (CO), which activate soluble guanylyl cyclase (sGC). Cyclic GMP is produced in response to odorants. Another type of GC, particulate GC (pGC), has been recently identified in the olfactory system; however, the role of the pGC pathway is not known. Since pGC plays a critical role in visual transduction, it could function in other sensory systems. In preliminary experiments, I found that various odorants elevated cGMP in isolated olfactory cilia due to activation of a pGC. The olfactory cilia, therefore, appears to provide an excellent model to study pGC. I will characterize the pGC, determining basal ATP dependence, calcium and calcium/calmodulin dependence, and the dependence of the activity on upstream G protein coupled signal. The cGMP level is determined by [125I]-cGMP radio- immunoassay (RIA). The generality of the odorant-induced cGMP response will be also investigated. Thereafter, I intend to purify the olfactory pGC by modifications of methodologies used for purification of retinal pGC. The kinetics of purified pGC will be intensively investigated using various enzyme study methods and compared to the one cloned olfactory pGC. These experiments will help understanding of function of the olfactory pGC, and in turn, understanding of the role of sensory pGC family.